And proclaim as you go, saying, ‘The kingdom of heaven is at hand.’ 8  Heal the sick, raise the dead, cleanse lepers, cast out demons. You received without paying; give without pay. Matthew 10:7-8 (ESV)

Everywhere Jesus went he manifested the reality of the kingdom of God by setting people free from demonic oppression. He commissioned his disciples to do the same, which is still in effect.

Deliverance from demons, like healing, is clear indicator of the presence of the King and the advance of his kingdom.

The Bible teaches us that evil spirits actually exist. Demons seek to capture, torment, and destroy people. The King came to set the captives free, give people peace, and protect them as the Good Shepherd. One of Jesus’ names is Redeemer. A redeemer is one who purchases the freedom of another in order to set them free. Jesus paid for our freedom with his blood.

And they *sang a new song, saying, "Worthy are You to take the book and to break its seals; for You were slain, and purchased for God with Your blood men from every tribe and tongue and people and nation. Revelation 5:9 (NASB) 

His death and resurrection sets people free from everything that would try to enslave them, so that they might serve God freely and wholeheartedly.

I also pray that you will understand the incredible greatness of God’s power for us who believe him. This is the same mighty power 20  that raised Christ from the dead and seated him in the place of honor at God’s right hand in the heavenly realms. 21  Now he is far above any ruler or authority or power or leader or anything else—not only in this world but also in the world to come. 22  God has put all things under the authority of Christ and has made him head over all things for the benefit of the church.Ephesians 1:19-22 (NLT) 

All power and authority was transferred to the risen Messiah King, which he uses to liberated Satan’s former captives. He does this through the power of the Holy Spirit.

But if it is by the Spirit of God that I cast out demons, then the kingdom of God has come upon you. Matthew 12:28 (ESV) 

Jesus gave authority over evil spirits to his disciples.

The seventy returned with joy, saying, "Lord, even the demons are subject to us in Your name." 18  And He said to them, "I was watching Satan fall from heaven like lightning. 19  "Behold, I have given you authority to tread on serpents and scorpions, and over all the power of the enemy, and nothing will injure you. Luke 10:17-19 (NASB)  

Evil spirits must obey when followers of Christ command them to leave. The Holy Spirit enforces our commands when we operate in the authority of Christ. When disciples of Christ cast out demons, it is a clear demonstration of God’s power and Christ’s authority.

Like healing, deliverance confirms the authenticity of the gospel message.

The early church carried forward this practice as part of its gospel message.

Now many signs and wonders were regularly done among the people by the hands of the apostles. And they were all together in Solomon’s Portico. 13  None of the rest dared join them, but the people held them in high esteem. 14  And more than ever believers were added to the Lord, multitudes of both men and women, 15  so that they even carried out the sick into the streets and laid them on cots and mats, that as Peter came by at least his shadow might fall on some of them. 16  The people also gathered from the towns around Jerusalem, bringing the sick and those afflicted with unclean spirits, and they were all healed. Acts 5:12-16 (ESV)  

And the crowds with one accord paid attention to what was being said by Philip when they heard him and saw the signs that he did. 7  For unclean spirits, crying out with a loud voice, came out of many who had them, and many who were paralyzed or lame were healed. Acts 8:6-7 (ESV)

Today people in the secularized West often try to explain away demonic activity as being a product of the ignorance of previous generations, believing that we can account for what the Bible calls the demonic by other scientific explanations. However, if we maintain that Jesus actually knew what he was talking about and that the Bible is inspired by the Holy Spirit, we must take demons seriously. Conversely, many people are terrified by the demonic, having gotten all their information from horror movies which glorify evil.

The reality is that demons exist, but they are under the authority of Christ and must obey Christ’s representatives.

How and when to cast out demons is a big topic, but you can read more by clicking here.) The important things to remember are that demons are real, Christ has already defeated them, followers of Christ have authority over them, the Holy Spirit backs up that authority, and casting them out is a sign of the presence of God’s kingdom. When we preach the gospel, we should expect to encounter demonic oppression in people and be prepared to use Christ’s authority to handle the situation. When we do that properly, it confirms the reality of Christ’s authority and the truth of the gospel.